Ocular micro tremor (omt) sensor, system and method

ABSTRACT

An eye sensor, system and method for measuring fixational eye movements of an individual&#39;s eyeball (e.g., ocular microtremors and microsaccades) to provide a variable voltage biosignal for measuring the individual&#39;s brain stem activity. The eye sensor comprises a sensor mounted on the individual&#39;s closed or opened eyelid so as to be deflected by the fixational eye movements of the eyeball. A shielded flexible ribbon assembly supplies the biosignal generated by the sensor to an amplifier located on the individual&#39;s skin where the biosignal is amplified. The amplifier is interconnected with a signal processor and a display by which graphical and numerical representations of the biosignal are made accessible to an anesthesiologist, intensivist or clinician. A method for analyzing the biosignal to determine the brainstem activity of a patient.

BACKGROUND OF THE INVENTION 1. Field of the Invention

This invention relates to an ocular micro tremor (OMT) sensor, systemand method which displays graphical and numerical representations of themicromovements of a patient's eyeball (i.e., the cornea/sclera) toprovide a healthcare worker (e.g., an anesthesiologist, intensivist orclinician) with an indication of the patient's brain stem activity oraltered brain stem state including his level of sedation, consciousnessand responsiveness prior to, during and after a medical or clinicalprocedure, such as, for example, when the patient is anesthetized duringan operation. The OMT sensor is thin and compliant and capable ofconforming to the shape of the patient's closed eyelid or being locatedin the tissue folds of the patient's open eyelid at which to beresponsive to the micromovements of the patient's eyeball.

2. Background Art

During the performance and treatment of many medical procedures andconditions, an anesthesia is administered so that a patient is sedatedand rendered unconscious. In some cases, the patient may be over-sedatedthroughout an operation which could permanently impact his neuralability and possibly cause brain stem death. In other cases, the patientmay be under sedated and immobilized without having the ability to alertmedical personnel to a level of consciousness which subjects the patientto pain. In still other cases, over-sedation of a patient may prolongthe duration of mechanical ventilation, and under-sedation can result inthe patient being subjected to unintended extubation.

For a long time, a primary source of information available to aclinician concerning the depth of anesthesia or sedation was limited tothe patient's somatic and autonomic response to physical and/or verbalstimuli. These responses are known to be susceptible to being alteredand influenced by neuromuscular blocking drugs, drugs affecting theautonomic nervous system, and the inconsistency of the stimuli. Thus,the presence or absence of these responses does not always accuratelycorrelate with conscious awareness and, therefore, can be inadequateindicators of the depth of the patient's unconscious state.

Sensors are known which are responsive to the micro eye movements of anindividual undergoing testing to provide a better indication of theindividual's level of sedation and brain stem activity. Sensors are alsoknown which are adhesively bonded over the patient's closed eyelid tosense large (i.e., gross) motions of the patient's eyeball. However, theknown sensors are relatively large, such that they are limited to beingused during surgery when the eyes of the individual being tested arefully closed and taped shut. Because small micro eye movements have anamplitude of about 500 nanometers, these motions are susceptible tobeing masked or altered by external electrical and electromagneticinterference as well as physical forces and biological artifacts.Therefore, what is needed now is an improved sensor and a sensor systemthat are capable of generating a clean biosignal that accuratelyreflects the ocular micromovements of the patient's eye ball (e.g.,having an amplitude of 40 micro meters or less) by reducing unwantedartifacts, both seismic and electrical, and by amplifying theinformation content of the biosignal without also amplifying theundesirable background noise. Moreover, to maximize its application, theimproved sensor should be of low cost, able to avoid contamination andcompact so as to be capable of being attached directly to theindividual's closed eyelid or in the tissue folds thereof at which to beresponsive to the micromovements while the patient is fully or partiallyasleep or awake and while his eyelid is fully closed, fully open orblinks between being opened and closed. In this same regard, the sensormust be sufficiently compliant so as to avoid applying uncomfortablefocused pressure forces to the patient's eye and be easily attached in aconvenient manner so as to be worn comfortably with the patient beingsubstantially unaware of its presence.

SUMMARY OF THE INVENTION

In general terms, an ocular micro tremor (OMT) sensor, system and methodare disclosed having an application for providing an anesthesiologist,intensivist, clinician, or the like, with a reliable indication of apatient's level of brain stem activity or altered brain stem stateincluding his level of sedation, responsiveness and consciousness priorto, during and following a medical procedure or evaluation such as inthe case of an anesthesia administered to the patient during anoperation. The OMT sensor includes an electrically active sensingelement such as, for example, a flexible piezo-active sensing elementthat can be attached directly over the patient's closed eyelid or in thetissue folds of his opened eyelid so as to be responsive to themicromotions of the patient's eyeball (i.e., the cornea/sclera) havingan amplitude of 40 micro meters or less. The OMT sensor also includes ashielded flexible ribbon assembly by which an alternating voltagebiosignal generated by the piezo-active sensing element is supplied to ashielded OMT signal amplifier. The amplified output of the OMT signalamplifier of the OMT sensor is supplied first to a signal processor andthen to a visual display which provides graphical and numericalrepresentations of the biosignal and the patient's brain stem activityand level of consciousness.

By way of a preferred embodiment, the flexible piezo-active sensingelement of the OMT sensor includes upper and lower thin filmpiezoelectric layers that are joined one above the other by anintermediate bonding agent. The outside of each of the upper and lowerpiezoelectric layers has an electrically conductive surface. Thepiezo-active sensing element of the OMT sensor is adapted to generatethe alternating voltage biosignal between the outside conductivesurfaces as the upper and lower piezoelectric layers thereof aredeflected in response to micromovements of the patient's eyeball. Toincrease its sensitivity and reduce the discomfort of the wearer, theflexible piezo-active sensing element is attached to the patient'seyelid so as to conform to the shape thereof.

The flexible ribbon assembly of the OMT sensor which extends between thepiezo-active sensing element and the OMT signal amplifier includes upperand lower non-conductive strips that are attached one above the other byan intermediate adhesive bonding layer. The flexible ribbon assembly isshielded from external electrical and electromagnetic interference byelectrically conductive coatings that lie on the outside of the upperand lower non-conductive strips. An electrically conductive trace runslongitudinally along the inside of each of the upper and lowernon-conductive strips such that the traces lie in spaced parallelalignment and in electrical isolation from one another and theelectrically conductive shielding coatings. The piezo-active sensingelement is sandwiched between the opposing upper and lowernon-conductive strips at the proximal end of the flexible ribbonassembly so that the electrically conductive outside surfaces of thesensing element lie in electrical contact with electrical terminalsformed at first ends of the conductive traces that run along the upperand lower strips. A flexible circuit board is sandwiched between theopposing upper and lower non-conductive strips at the distal end of theflexible ribbon assembly so as to lie in electrical contact withelectrical terminals formed at the opposite ends of the conductivetraces. The flexible circuit board at the distal end of the flexibleribbon assembly is coupled to an electrical connector block that islocated at the interior of the OMT signal amplifier. Accordingly, thealternating voltage biosignal generated by the piezo-active sensingelement of the OMT sensor is supplied to the OMT signal amplifier by wayof the electrically conductive traces that run along the upper and lowernon-conductive strips of the flexible ribbon assembly.

The OMT signal amplifier of the OMT sensor to which the alternatingvoltage biosignal is supplied from the flexible piezo-active sensingelement and the shielded flexible ribbon assembly includes anelectrically conductive housing that shields the biosignal from externalelectrical and electromagnetic interference. The amplifier housing isattached by an electrically conductive adhesive patch to the patientskin. A printed circuit board which lies at the bottom of and within theamplifier housing is coupled to a grounding electrode that extendsthrough the housing to be held against the patient's skin. Theelectrically conductive traces which run along the flexible ribbonassembly and carry the OMT biosignal from the sensing element areconnected to the printed circuit board for amplification by means of theaforementioned connector block located within the housing of the OMTsignal amplifier. First and second electrically conductive mesh pillowslie inside the amplifier housing so as to contact respective ones of theelectrically conductive shielding coatings that lie on the outside ofthe upper and lower non-conductive strips of the ribbon assembly. Themesh pillows lie in circuit paths by which the shielding coatings of theribbon assembly are connected to each other and to electrical ground atthe patient's skin by way of the grounding electrode through the bottomof the amplifier housing. The output of the OMT signal amplifier issupplied from the printed circuit board thereof to the signal processorby way of either a shielded cable from the amplifier housing or awireless transmitter that is located within the amplifier housing andcommunicates with a remote transceiver of the signal processor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an anesthesiologist watching a display to view graphicaland numerical representations of an electrical biosignal which areindicative of the brain stem activity and level of consciousness of asedated patient who undergoes an operation while wearing the ocularmicro tremor (OMT) sensor of the invention;

FIG. 2 shows a multiple layer piezo-active sensing element of the OMTsensor of FIG. 1 attached to a closed eyelid of the patient at which tobe responsive to micromovements of the patient's eyeball so that thebiosignal is generated by the sensing element and supplied to an OMTsignal amplifier mounted at the eye;

FIG. 3 is a cross-section of the OMT sensor taken along lines 3-3 ofFIG. 2;

FIG. 3A is an enlarged detail taken from FIG. 3 showing the multiplelayer piezo-active sensing element of the OMT sensor lying on the closedeyelid of the patient;

FIG. 4 is a cross-section of the OMT sensor taken along lines 4-4 ofFIG. 3;

FIG. 5 shows the piezo-active sensing element of the OMT sensor of FIG.1 located within the tissue folds of the patient's open eyelid at whichto be responsive to the micromovements of the patient's eyeball so thatthe OMT biosignal is generated by the sensing element and supplied tothe OMT signal amplifier;

FIG. 6 is a cross-section of the OMT sensor taken along lines 6-6 ofFIG. 5;

FIG. 7 shows the OMT sensor of FIG. 5 including a wireless OMT signalamplifier;

FIG. 8 shows a preferred embodiment for the multiple layer piezo-activesensing element of the OMT sensor of FIG. 1 which is deflected inresponse to the micromovements of the patient's eyeball to which thesensing element is responsive in order to generate the OMT biosignal;

FIGS. 9 and 10 show the multiple layer piezo-active sensing element ofFIG. 8 being deflected in different directions to generate the OMTbiosignal depending upon the direction of the micromovements of thepatient's eyeball;

FIG. 11 shows the OMT signal amplifier of the OMT sensor of FIG. 2 beingdetachably connected to a grounding electrode that is attached by anelectrically conductive adhesive patch to the patient's skin;

FIG. 12 is a cross-section of the OMT signal amplifier taken along lines12-12 of FIG. 11;

FIG. 13 is an exploded view of a shielded flexible ribbon assembly ofthe OMT sensor by which the multiple layer piezo-active sensing elementof FIGS. 8-10 is electrically connected to the OMT signal amplifier ofFIG. 12;

FIG. 14 is a top view of the shielded flexible ribbon assembly of FIG.13 connected at a proximal end thereof to the multiple layerpiezo-active sensing element of FIGS. 8-10 and at a distal end to anelectrical connector block of the OMT signal amplifier of FIG. 12;

FIG. 15 is a cross-section of the shielded flexible ribbon assemblytaken along lines 15-15 of FIG. 14;

FIG. 16 is a cross-section of the shielded flexible ribbon assemblytaken along lines 16-16 of FIG. 14;

FIG. 17 is a block diagram illustration of a communication system inwhich the OMT sensor of FIG. 2 is coupled to a signal processor and tothe display of FIG. 1;

FIG. 18 is a block diagram illustration of a communication system inwhich the OMT sensor of FIG. 7 is coupled to a signal processor and tothe display of FIG. 1 over a wireless communication path;

FIG. 19 shows another embodiment for an ocular micro tremor (OMT) sensorwhich includes a mechanical force transmitting arm actuator that isattached to the patient's eyelid at which to be deflected in response tomicromotions of the patient's eyeball transmitted thereto so that anelectrical biosignal can be generated by a piezo-active sensing elementof the sensor;

FIGS. 20-22 show a different embodiment for an ocular micro tremor (OMT)sensor having a tubular surface-mounted piezo-active sensing elementthat is located within the folds of the patient's eyelid at which toundergo a shape distortion in response to micromovements of thepatient's eyeball transmitted thereto for generating an electricalbiosignal;

FIG. 23 is an enlarged detail of a tubular-to-planar strain reliefadapter taken from the OMT sensor shown in FIG. 20; and

FIG. 24 shows yet another embodiment for an ocular micro tremor (OMT)sensor having a cylindrical force transmitting actuator that is locatedwithin the folds of the patient's eyelid at which to undergo a shapedistortion in response to micromovements of the patient's eyeballtransmitted thereto so that an electrical biosignal can be generated bya piezo-active sensing element of the sensor.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring initially to FIG. 1 of the drawings, there is shown ahealthcare practitioner, such as an anesthesiologist, intensivist,clinician, or the like, monitoring a patient who is unconscious andsedated. The (e.g., anesthesiologist) is able to monitor the brain stemactivity and altered brain stem state of the patient to measure hislevel of sedation, consciousness and responsiveness by virtue of acompact, low cost and highly compliant ocular micro tremor (hereinafter“OMT”) sensor. The OMT sensor 1 is shown in FIG. 1 positioned at theeyelid of the patient so as to be advantageously able to reliably sensethe micro tremors of the patient's eyeball (i.e., micromovements of thecornea/sclera which have an amplitude of 40 micrometers or less) inorder to provide the anesthesiologist with an indication of thepatient's awareness during a medical procedure (e.g., in an operatingroom or intensive care facility).

However, it is to be understood that the OMT sensor 1 herein disclosedcan also be used to monitor and provide an indication of the alertness,awareness, arousal, diagnosis of injury and behavior modification of anindividual in both medical and industrial environments. The OMT sensor 1is also capable of monitoring any condition or circumstance in which itis desirable to obtain a measurement of brain stem activity of anindividual to be compared against a known reference. To this end, theOMT sensor 1 of this invention is advantageously capable of beingattached directly over the patient's closed eyelid or in the tissuefolds adjacent the patient's eyelid. While the OMT sensor 1 willsometimes be referred to herein as having particular application for useby a patient in the care of an anesthesiologist or similar healthcarepractitioner, it is to be once again understood that the sensor can alsobe used in an industrial or other non-medical environments to test thealertness of one wishing to drive, operate machinery, perform complextasks, etc.

The OMT sensor 1 of FIG. 1 includes an electrically active sensingelement which, according to a preferred embodiment of this invention, isa multi-layer piezo-active sensing element (designated 16 in FIGS. 8-10)that is coupled to an OMT signal amplifier 3 by way of a shieldedflexible ribbon assembly 5. The output of the OMT signal amplifier 3 ofthe OMT sensor 1 is supplied to a signal processor (designated 9 andbest shown in FIG. 17) by means of a shielded cable 7. The signalprocessor, in turn, is electrically connected to a visual display 10.The details of the multiple layer piezo-active sensing element 16, theflexible ribbon assembly 5, as well as the OMT signal amplifier 3 towhich the sensing element 16 is coupled to form the OMT sensor 1 will bedescribed in greater detail hereinafter.

FIG. 1 shows the visual display 10 which communicates with the signalprocessor 9 (of FIG. 17) to display for the anesthesiologist informationgenerated by the OMT sensor 1 when the patient is unconscious andsedated. However, the display 10 can also provide information during apreliminary baseline test when the patient is semi-conscious or fullyconscious, alert and not sedated. By way of example only, the display 10shows an OMT biosignal 12 that is generated by the OMT sensor 1 inresponse to micromovements of the patient's eyeball. The shape andamplitude of the OMT biosignal 12 provide a graphical representation ofthe patient's brain stem activity and his level of consciousness over aparticular sampling time. The OMT biosignal 12 is generally analternating voltage waveform that is reflective of the micromovements ofthe patient's eyeball to which the OMT sensor 1 is responsive by way ofthe patient's eyelid. In addition, the display 10 also shows a discretereference number 14 to be computed by the signal processor for easyvisual reference by the anesthesiologist. By way of example, thereference number 14 being displayed is dependent upon the micromovementsof the eyeball and the corresponding frequency of the waveform of theOMT biosignal 12 in order to provide another indication of the patient'sbrain stem activity and his level of consciousness, sedation andresponsiveness.

Turning now to FIGS. 2-4 of the drawings, the multiple layerpiezo-active sensing element 16 (of FIGS. 8-10) of the OMT sensor 1 isshown attached to a closed eyelid of an individual, such as a patientwho is heavily sedated while undergoing an operation in an operatingroom. However, and as indicated previously, the OMT sensor 1 can also beattached to the eyelid of an individual undergoing evaluation in anindustrial or other non-medical environment. In this case, the patient'seyelid is held closed prior to the attachment of the sensing element 16.A double-sided pressure sensitive adhesive patch (designated 100 inFIGS. 3A and 13) is used to hold the sensing element 16 of the OMTsensor 1 against the patient's closed eyelid above the patient's eyeballat which to be responsive to the micromovements of the eyeball andthereby provide the OMT biosignal 12 (of FIG. 1) by way of the flexibleribbon assembly 5 to the OMT signal amplifier 3. The OMT signalamplifier 3 provides an amplified analog OMT biosignal 12 to the signalprocessor so that both graphical and numerical representations of thepatient's brain stem activity including his level of consciousness,sedation and responsiveness are visually available to theanesthesiologist at the display 10.

However, there are instances when it would be desirable to be able touse the OMT sensor 1 of this invention to measure and indicate thepatient's brain stem activity and his level of consciousness when hiseyelid is fully or partially open. In this case, and referring to FIGS.5 and 6 of the drawings, the OMT sensor 1 is shown attached to thepatient's rolled up eyelid. For example, it is preferable to use the OMTsensor 1 in the manner shown in FIGS. 5 and 6 at those times when thepatient is lightly or moderately sedated, when the patient's eyelid isalternately being opened and closed, or when the patient's eyelid isfully open, such as while a preliminary baseline test is beingconducted.

By virtue of the foregoing, the patient's brain stem activity and levelof consciousness can be continuously monitored to enable intervention bythe anesthesiologist or other healthcare practitioner when necessaryprior to, during and following a medical procedure (e.g., an operation)when the patient will be sedated for some portion of the procedure.Because the OMT sensor 1 including the multiple layer piezo-activesensing element 16 (of FIGS. 8-10) and the flexible ribbon assembly 5 isthin and compliant, the sensor 1 may be advantageously attached, asshown in FIGS. 5 and 6, between the tissue folds of the patient's openedeyelid at which the piezo-active sensing element 16 of sensor 1 isresponsive to the micromovements of the patient's eyeball.

In FIGS. 1-6, the OMT signal amplifier 3 of the OMT sensor 1 has beendescribed as being connected to a signal processor (designated 9 in FIG.17) by means of a shielded cable 7. However, as shown in FIG. 7 of thedrawings, it is within the scope of this invention for the amplifier 3to be replaced by a wireless OMT signal amplifier 3-1. In this case, theshielded cable (designated 7 in FIG. 5) will now be eliminated.Moreover, the wireless OMT signal amplifier 3-1 is provided with ananalog-to-digital converter (designated 110 in FIG. 18) and aconventional wireless transmitter (designated 116 in FIG. 18), and thesignal processor (designated 9-1 in FIG. 18) is provided with acomplementary transceiver 118. In this manner, the amplified OMTbiosignal can be transmitted from the OMT signal amplifier 3-1 to thesignal processor 9-1 at a remote location and over a wirelesscommunication path.

Details of the multiple layer piezo-active sensing element 16 of theocular micro tremor (OMT) sensor 1 shown in FIGS. 1-6 are now disclosedwhile referring to FIGS. 8-10 of the drawings. As was previouslyexplained, the sensing element 16 of the OMT sensor 1 is adhesively heldagainst the moving surface of the patient's opened or closed eyelid(represented generally by reference numeral 20 in FIGS. 8-10) so as tobe responsive to the micromovements of the patient's eyeball which havean amplitude of 40 micro meters or less and thereby provide acorresponding alternating voltage OMT biosignal to thesoon-to-be-described OMT signal amplifier (designated 3 in FIG. 1).

According to the preferred embodiment, the multiple layer piezo-activesensing element 16 of the OMT sensor 1 has a thin planar top layer 22, athin planar bottom layer 24 and an intermediate bonding agent 26 (e.g.,epoxy) located therebetween to hold the top and bottom layers 22 and 24together one above the other. A first electrically conductive (e.g.,copper) surface 28 is applied to the outside of a first flexiblepiezoelectric (e.g., PVDF) film 30 from the planar top layer 22 of thepiezo-active sensing element 16 to establish a first output terminal. Asecond electrically conductive (e.g., copper) surface 32 is applied tothe outside of a second flexible piezoelectric film 34 from the planarbottom layer 24 of sensing element 16 to establish a second outputterminal. The inside of each of the first and second piezoelectric films30 and 34 of the top and bottom layers 22 and 24 of sensing element 16which face one another are held in opposing alignment by theintermediate bonding agent 26.

The length and width of the piezoelectric films 30 and 34 may be largerthan the respective length and width of the first and second conductivesurfaces 28 and 32 so as to avoid undesired electrical communicationbetween the surfaces 28 and 32. The ideal thickness of the multiplelayer piezo-active sensing element 16 shown in FIGS. 8-10 is between 20to 150 microns.

The first and second flexible piezoelectric films 30 and 34 of the thinplanar top and bottom layers 22 and 24 of the piezo-active sensingelement 16 of the OMT sensor 1 are conventional and are adapted togenerate a voltage as the sensing element is deflected in response tothe micromovements of the patient's eyeball which create a correspondingmotion through the eyelid 20 above which the sensing element 16 isattached. That is to say, the normally planar first and secondpiezoelectric films 30 and 34 are deformed and deflected by themovements of the patient's eyelid 20 caused by the micromovements of theeyeball. In the case where the multiple layer piezo-active sensingelement 16 is at rest as shown in FIG. 8, no voltage is generated by thepiezoelectric films 30 and 34 between the first and second outputterminals at the outside conductive surfaces 28 and 32. In the casewhere the piezo-active sensing element 16 is deflected in a firstdirection by the movement of the patient's eyelid 20 in the same firstdirection as shown in FIG. 9, a positive voltage is generated by thepiezoelectric films 30 and 34 between the output terminals at theoutside conductive surfaces 28 and 32. In the case where the sensingelement 16 is deflected in an opposite direction by the movement of thepatient's eyelid 20 in the same opposite direction as shown in FIG. 10,a negative voltage is generated by the piezoelectric films 30 and 34between the output terminals at the outside conductive surfaces 28 and32.

Because the micromovements of the patient's eyeball typically occur at ahigh frequency and with a variable intensity, the multiple layerpiezo-active sensing element 16 of the OMT sensor is likely to flex backand forth at a correspondingly high frequency. The amplitude, positiveor negative direction, and frequency of the micromovements to which thesensing element 16 is responsive are reflected graphically andnumerically by the OMT biosignal 12 and the reference number 14 that arevisually accessible to the anesthesiologist at the display 10 of FIG. 1.

The preferred electrically active sensing element for the OMT sensor 1has been described while referring to FIGS. 8-10 as being a flexiblemulti-layer piezo-active sensing element 16 that is adapted to generatea voltage in response to the sensing element being deflected by themicromovements of the patient's eyeball. However, the sensing element ofthe OMT sensor 1 may also be other electrically active devices, such asa variable resistance element (e.g., a strain gauge), a variablecapacitor, accelerometer or a variable inductor, the outputs of whichwill be indicative of the micromovements of the eyeball of theindividual undergoing testing. What is more, it is to be expresslyunderstood that the pair of flexible piezoelectric films 30 and 34 ofthe multi-layer piezo-active sensing element 16 can be replaced by asingle flexible piezoelectric film that has at the top and bottomthereof electrically conductive surfaces which lie thereon to establishthe aforementioned first and second output terminals between which theOMT biosignal is generated. The aforementioned single piezoelectric filmmay be seated on a supportive non-conductive substrate.

In one case, it has been found that attaching a conventional ocularmicro tremor sensor to a patient's eyelid may result in a focusedpressure being applied to the eyelid which creates a depression in thepatient's eyeball. The sometimes intrusive nature of the conventionalsensor applying a focused pressure to the patient's eyeball can, overtime, cause patient discomfort. In this and other cases, a conventionalsensor may require additional intervention and controls to ensure itsproper position placement in order to be capable of responding to thepatient's eye motions. What is even more, the patient may resist wearingthe conventional sensor to avoid the discomfort caused by the pressurebeing applied to his eyeball.

Referring specifically to FIGS. 3 and 3A of the drawings, the idealposition is described at which the flexible multi-layer piezo-activesensing element 16 of the OMT sensor 1 shown in FIGS. 8-10 is heldagainst the patient's fully closed eyelid. As an important feature ofthe invention, the flexible sensing element 16 is sufficiently thin (asexplained when referring to FIGS. 8-10) and compliant to assume agenerally arcuate (i.e., curved) configuration in order to conform tothe shape of the patient's eyelid when the sensing element is attachedthereto by means of the double-sided pressure sensitive adhesive patch100. That is, the sensing element 16 surrounds at least some of thepatient's closed eyelid and is sized so as to be large enough to coverangular excursions of the eyeball yet small enough to be placed withinthe eye socket.

In this regard, the top and bottom planar layers 22 and 24 of thepiezo-active sensing element 16 of the OMT sensor 1 of this inventionwill cover a relatively large surface area of the eyelid so as to beresponsive to a full range of motion of the patient's eyeballtransmitted through the eyelid. Moreover, the pressure applied to theeyelid by the sensing element 16 is more uniformly distributed aroundthe eyelid than conventional focused pressure sensing elements.Accordingly, the flexible piezo-active sensing element 16 will be morecomfortable to wear for longer periods, is less costly and easier toaccurately position at the eyelid to achieve a reliable response thanconventional focused pressure sensing elements. Therefore, the OMTsensor 1 can be comfortably fitted to the patient such that the sensingelement 16 thereof is unlikely to be noticed or objected to.

The flexible multiple layer piezoelectric sensing element 16 is shown inFIG. 3A conforming to the shape of the patient's eyelid and beingcoupled to the flexible ribbon assembly 5 of the OMT sensor 1. As willbe described in greater detail when referring to FIGS. 16-18, thesensing element 16 is surrounded by upper and lower strips 62 and 64 ofthe ribbon assembly 5. Electrically conductive coatings 70 and 72 layover the outside surfaces of respective ones of the upper and lowerstrips 62 and 64 to provide the ribbon assembly 5 with shielding inorder to avoid subjecting the biosignal generated by the sensing element16 and transmitted via the flexible ribbon assembly 5 to electrical andelectromagnetic noise and other interference.

The details of the OMT signal amplifier 3 of the OMT sensor 1 to whichthe OMT biosignal that is generated by the multiple layer piezo-activesensing element 16 is supplied are described while referring to FIGS. 11and 12 of the drawings. To isolate the electrical components of theamplifier 3 and thereby prevent environmental electrical andelectromagnetic interference from altering the information contained bythe OMT biosignal, the OMT signal amplifier 3 is provided with aconductive shielded housing 38 having a removable lid 40. The multiplelayer piezo-active sensing element 16 of the OMT sensor 1 iselectrically connected to the amplifier 3 by way of the shieldedflexible ribbon assembly 5 (best shown in FIGS. 13-16). It is preferablethat the flexible ribbon assembly 5 be given slack and/or be looselyconnected between the piezo-active sensing element 16 and the OMT signalamplifier 3 so as to avoid applying loads or pulling forces to thepatient's eyelid and thereby inducing a possible unintended response bythe sensing element 16.

An amplifier grounding electrode 44 having a flat conductive base 45 isheld against the patient's skin by an electrically conductive adhesivefoam patch 46 (e.g., a common EKG electrode patch) that is attached tothe bottom of the amplifier housing 38 and covered by a pull-off releasefilm strip (not shown). Once the release strip is removed, the adhesivepatch 46 is attached to the patient's skin (e.g., at one side of hisforehead) so that the OMT signal amplifier 3 will be located adjacentthe piezo-active sensing element 16 and thereby avoid applying a pullingforce against the ribbon assembly 5. An electrical receptacle 56 insidethe amplifier housing 38 is then snapped into detachable matingengagement with the amplifier electrode 44 so that the base 45 ofelectrode 44 lies flush against the patient's skin. The adhesive patch46 anchors the OMT signal amplifier 3 in place against the patient'sskin and prevents a displacement thereof relative to the ribbon assembly5 during the period when the patient's ocular micromovements are beingmonitored. It should be recognized that other conventional electricaland mechanical amplifier attachment means can be substituted for theelectrically conductive adhesive foam patch 46.

To ensure that the amplified alternating voltage signals generated bythe OMT signal amplifier 3 are not altered by the environment, it isimportant that both the electrically conductive housing 38 of the OMTsignal amplifier 3 and the electrically conductive shielding coatings 70and 72 that cover the outside surfaces of the upper and lower strips 62and 64 of the flexible ribbon assembly 5 are connected to electricalground. To this end, electrical paths are established to ground from thecoatings 70 and 72 of the flexible ribbon assembly 5 and the housing 38of the amplifier 3 to the patient's skin at the amplifier groundingelectrode 44 which is held in place against the skin by the electricallyconductive adhesive patch 46. Details of these electrical paths toground at the patient's skin are described below.

As is best shown in FIG. 12, the shielded flexible ribbon assembly 5 ofthe OMT sensor 1 is connected at a proximal end thereof to the multiplelayer piezo-active sensing element 16 (best shown in FIG. 13) and at theopposite distal end to an electrical connector block 48 that is locatedat the interior of the amplifier housing 38. A first electricallyconductive (e.g., mesh) and resilient pillow 50 is positioned withinhousing 38 so as to lie between the removable lid 40 thereof and theelectrically conductive shielding coating 70 that runs over the top ofthe ribbon assembly 5. A second electrically conductive and resilientpillow 52 is positioned within housing 38 so as to lie between theelectrically conductive coating shielding 72 that runs over the bottomof the ribbon assembly 5 and a printed circuit board 54 that ispositioned at the bottom of the housing 38 of the OMT signal amplifier3. The aforementioned amplifier grounding electrode 44 is detachablyconnected to the signal amplifier 3 through the bottom of housing 38 andto the printed circuit board 54 at the electrical receptacle 56, suchthat the flat conductive base 45 of electrode 44 is connected to groundagainst the patient's skin.

The first and second electrically conductive pillows 50 and 52 lie inelectrical contact with respective ones of the aforementionedelectrically conductive shielding coatings 70 and 72 at the top andbottom of the flexible shielded ribbon assembly 5. Thus, theelectrically conductive shielding coating 70 at the top of the flexibleribbon assembly 5 is connected to ground at the patient's skin by way ofa first electrical path to ground that includes the first conductivepillow 50, the electrically conductive shielded amplifier housing 38, afirst jumper wire 60 that connects housing 38 to the electricalreceptacle 56, and finally the amplifier grounding electrode 44 and theelectrode base 45 lying against the patient's skin. The electricallyconductive shielding coating 72 at the bottom of the flexible ribbonassembly 5 is also connected to ground by way of a second electricalpath to ground that includes the second conductive pillow 52 and asecond jumper wire 61 that connects pillow 52 to the electricalreceptacle 56, and finally the amplifier grounding electrode 44 and thebase 45 thereof against the user's skin. In this same regard, it may beappreciated that the conductive shielding coatings 70 and 72 at the topand bottom of the flexible ribbon assembly 5 are electrically connectedto one another by way of the electrically conductive mesh pillows 50 and52 and the electrically conductive shielded amplifier housing 38.

The resilient characteristic of the electrically conductive (e.g., mesh)pillows 50 and 52 which overlay the electrically conductive shieldingcoatings 70 and 72 of the flexible ribbon assembly 5 accommodate andabsorb bending forces to which the ribbon assembly is subjected. Thepillows 50 and 52 also support the ribbon assembly 5 within theamplifier housing 38 and suspend the ribbon assembly above the printedcircuit board 54 so as to lie in axial alignment with the electricalconnector block 48. The electrical connector block 48 to which thedistal end of the ribbon assembly 5 is connected is, in turn,electrically connected to the printed circuit board 54 by way of anupstanding connector post 58. The printed circuit board 54 containsconventional signal conditioning and amplifier circuitry by which theOMT alternating voltage biosignal carried by the flexible ribbonassembly 5 is amplified (ideally by a factor of at least ten). Anamplified analog OMT biosignal is supplied from the OMT signal amplifier3 shown in FIG. 12 to the signal processor and display of FIG. 17 bymeans of the shielded output cable 7 that extends from the printedcircuit board 54 and outwardly through a side of the amplifier housing38. However, as earlier explained the OMT biosignal may also betransmitted from the amplifier to the signal processor over a wirelesscommunication path illustrated in FIG. 18.

Referring concurrently to FIGS. 13-16 of the drawings, details are nowprovided of the shielded flexible ribbon assembly 5 which iselectrically connected at the proximal end thereof to the multiple layerpiezo-active sensing element 16 (previously described while referring toFIGS. 8-10) and at the opposite distal end to the OMT signal amplifier 3(as described while referring to FIG. 12). The flexible ribbon assembly5 is disposed in surrounding engagement with and connected between thefirst and second (i.e., top and bottom) electrically conductive surfaces28 and 32 of the piezo-active sensing element 16 and the electricalconnector block 48 that is held (by the connector post 58) above theprinted circuit board 54 that is positioned inside and at the bottom ofthe shielded housing 38 of the OMT signal amplifier 3 shown in FIG. 12.

The shielded ribbon assembly 5 of the OMT sensor 1 includes upper andlower elongated and compliant strips 62 and 64 that are attached oneabove the other. By way of example, the bottom of the upper strip 62 andthe top of the lower strip 64 are bonded face-to-face one another by aconventional thin layer of adhesive (designated 65 in FIG. 15). Each ofthe upper and lower strips 62 and 64 of ribbon assembly 5 includes alayer 66 and 68 that is manufactured from an electrical insulatingpolyimide or any other suitable non-conductive material. Both the topand the bottom of each of the non-conductive layers 66 and 68 of theupper and lower strips 62 and 64 are initially covered by anelectrically conductive (e.g., aluminum or gold) coating.

As is best shown in FIG. 15, the conductive coatings 70 and 72 whichcover the outwardly facing top of the non-conductive layer 66 of theupper strip 62 and the outwardly facing bottom of the non-conductivelayer 68 of the lower strip 64 of the flexible ribbon assembly 5 areleft intact to create shielding surfaces. The shielding coatings 70 and72 were previously described while referring to FIG. 12 as beingconnected to each other and to ground at the individual's skin to shieldthe ribbon assembly 5 against electrical and electromagnetic energy thatmight interrupt or distort the biosignal generated by the piezo-activesensing element 16 of the OMT sensor 1 and supplied to the OMT amplifier3 by ribbon assembly 5.

As is best shown in FIG. 13, portions of the conductive coatings whichinitially cover the inwardly facing bottom of the non-conductive layer66 of the upper strip 62 and the opposing inwardly facing top of thenon-conductive layer 68 of the lower strip 64 are etched away to leaverespective longitudinally extending electrically conductive traces 74and 76 running along the non-conductive layers 66 and 68 of the upperand lower strips 62 and 64. During the aforementioned etching process,pairs of relatively wide electrically conductive terminals 78, 79 and80, 81 are formed at first and opposite ends of each of the conductivetraces 74 and 76. With the upper and lower strips 62 and 64 of theshielded ribbon assembly 5 bonded together by the intermediate adhesivelayer 65 (of FIG. 15), the longitudinally extending electricallyconductive traces 74 and 76 formed on the bottom and on the top of theopposing insulating layers 66 and 68 of the upper and lower strips 62and 64 lie in parallel alignment and in electrical isolation from oneanother. The aforementioned etching process is a preferred technique forforming the electrically conductive traces 74 and 76. However, it shouldbe understood that other conventional techniques can be used to form thetraces 74 and 76 on the electrically insulating layers 66 and 68.

As is best shown in FIG. 15, the multi-layer piezo-active sensingelement 16 is sandwiched between first ends of the upper and lowerstrips 62 and 64 at the proximal end of the flexible ribbon assembly 5.More particularly, a first electrically conductive pad 82 is adhesivelybonded between the terminal 78 formed at a first end of the trace 74 onthe bottom of the upper strip 62 and the first electrically conductivesurface 28 at the top of the piezo-active sensing element 16. A secondelectrically conductive pad 83 is adhesively bonded between the secondelectrically conductive surface 32 which lies at the bottom of thepiezo-active sensing element 16 and the terminal 80 formed at a firstend of the trace 76 on the top of the lower strip 64. The terminals 78and 80 at the first ends of traces 74 and 76 and the first and secondconductive pads 82 and 83 on the top and the bottom of the sensingelement 16 are all aligned with one another in a stack at the proximalend of the flexible ribbon assembly 5.

A third electrically conductive pad 84 is adhesively bonded between theterminal 79 formed at the opposite end of the trace 74 on the bottom ofthe upper strip 62 and an opposing upper terminal 86 formed on the topof a flexible transition circuit board 88 (of FIG. 13). The circuitboard 88 is sandwiched between opposite ends of the upper and lowerstrips 62 and 64 at the distal end of the flexible ribbon assembly 5. Afourth electrically conductive pad 85 is adhesively bonded between theterminal 81 formed at the opposite end of the trace 76 on the top of thelower strip 64 and an opposing lower terminal 90 formed on the bottom ofthe flexible transition circuit board 88. The terminals 79 and 81 at theopposite ends of the traces 74 and 76, the third and fourth conductivepads 84 and 85 above and below the circuit board 88, and the opposingupper and lower terminals 86 and 90 of the circuit board 88 are allaligned with one another in a stack at the distal end of the flexibleribbon assembly 5.

The upper terminal 86 of the transition circuit board 88 (i.e., a firstoutput terminal of the ribbon assembly 5) is electrically connected tothe electrical connector block 48 that is surrounded by the electricallyconductive shielded housing 38 of the OMT signal amplifier 3 (of FIG.12) by way of a first conductive trace 92 lying on the top of circuitboard 88 and a first electrical contact 94 of connector block 48. Thelower terminal 90 of the transition circuit board 88 (i.e., a secondoutput terminal of the ribbon assembly 5) is electrically connected tothe connector block 48 by way of a second conductive trace 96 lying onthe bottom of circuit board 88 and a second electrical contact 98 ofconnector block 48. As was previously explained while referring to FIG.12, the electrical connector block 48 is electrically connected to theprinted circuit board 54 that lies at the bottom of the housing 38 ofOMT signal amplifier 3. Therefore, it may be appreciated that thealternating voltage biosignal generated by the multiple layerpiezo-active sensing element 16 of the OMT sensor 1 is transmitted fromthe first and second electrically conductive surfaces 28 and 32 at thetop and at the bottom of sensing element 16 to the OMT signal amplifier3 by way of the electrically conductive traces 74 and 76 which run alongthe upper and lower strips 62 and 64 between the proximal and distalends of the shielded flexible ribbon assembly 5.

It may be appreciated that the electrically conductive trace 74 whichruns along the bottom of the insulating layer 66 of the upper strip 62of the flexible ribbon assembly 5 is electrically isolated from theshielding coating 70 that covers the top of the insulating layer 66.Likewise, the electrically conductive trace 76 which runs along the topof the insulating layer 68 of the lower strip 64 of the flexible ribbonassembly 5 is electrically isolated from the shielding coating 72 thatcovers the bottom of the insulating layer 68. Moreover, the shieldingcoatings 70 and 72 that cover the top of the insulating layer 66 and thebottom of the insulating layer 68 of the upper and lower strips 62 and64 completely surround the ribbon assembly 5 and enclose theelectrically conductive traces 74 and 76 thereof as well as thepiezo-active sensing element 16 lying therebetween so as to avoid analteration of the alternating voltage biosignal as could be caused byexternal electrical and electromagnetic interference.

The previously mentioned double-sided pressure sensitive adhesive patch100 is attached at one side thereof to the outwardly facing bottom ofthe lower strip 64 of the flexible shielded ribbon assembly 5. Theopposite side of the adhesive patch 100 is covered by pull off releasefilm strip 42. When the release strip 42 is pulled off and removed fromthe adhesive patch 100, the OMT sensor 1 including the flexible ribbonassembly 5 and the multi-layer piezo-active sensing element 16 that issandwiched between the upper and lower strips 62 and 64 at the proximalend of ribbon assembly 5 can be adhesively attached to the patient'seyelid in the manner described above while referring to FIGS. 2-6 topermit the ocular micromotions of the eyeball of the patient to besensed, amplified, processed and displayed.

By virtue of the shielded flexible ribbon assembly 5 herein disclosed,the multiple layer piezo-active sensing element 16 can be substantiallyisolated from mechanical forces that might otherwise be transmittedthereto from the OMT signal amplifier 3. By way of example, muscularactions, seismic activity and other mechanical motions and vibrationscould introduce unwanted artifact noise to the alternating voltagebiosignal produced by the sensing element 16. To this end, a minimumflexural rigidity depending upon the dimensions and material electricityof the ribbon assembly 5 are preferable in order to avoid thetransmission of such mechanical forces to the piezo-active sensingelement 16 via ribbon assembly 5.

To this end and by way of example only, the ideal thickness of theribbon assembly is less than or equal to 25 microns, while the idealwidth is about 4-8 mm. The ideal flexural rigidity of the flexibleribbon assembly 5 is less than or equal to 10×10⁻⁴ lbs⁻⁴-in⁴. Asindicated earlier, the flexible ribbon assembly 5 should be providedwith slack or strain relief to avoid pulling on the OMT sensing element16. That is, the length of the ribbon assembly 5 should ideally be atleast 5% longer than the straight line distance between the piezo-activesensing element 16 and the amplifier 3 of the OMT sensor 1.

FIG. 17 of the drawings shows the ocular micro tremor (OMT) sensor 1 ofthis invention connected to the previously mentioned signal processor 9.The processor 9 should be capable of filtering the amplified OMTbiosignal and eliminating artifacts (such as those caused by gross eyemovements and electrical or electromagnetic interference), analyzing theremaining signal and frequency information, and displaying the result atthe display 10. More particularly, and as previously disclosed, the OMTalternating voltage biosignal generated in response to a deflection ofthe first and second piezoelectric films (30 and 34 of FIGS. 8-10) ofthe multiple layer piezo-active sensing element 16 is first supplied toand amplified by the OMT signal amplifier 3. One signal processor 9which is suitable to be connected to the OMT signal amplifier 3 toreceive the amplified biosignal and perform the aforementioned processorfunctions is shown and described in U.S. Pat. No. 7,011,410 issued Mar.14, 2006, the details of which are incorporated herein by reference.Therefore, only a brief description of the signal processor 9 will beprovided below.

The amplified alternating voltage OMT biosignal is supplied from the OMTsignal amplifier 3 to an analog to digital (A/D) converter 110 of thesignal processor 9 of FIG. 17 by the shielded cable 7 connectedtherebetween. The A/D converter 110 converts the analog alternatingvoltage biosignal to a digital signal to facilitate processing. Thedigital signal produced by A/D converter 110 is supplied to a digitalisolator 112 which isolates the information content of the OMT biosignalfrom interference that might be produced by a source of power needed todrive the hardware required to perform the signal processing.

Frequency and amplitude bandpass filters 114 are used to provide theinformation to the anesthesiologist at the display 10 (of FIG. 1) whichis connected to processor 9. By way of example, the filters 114 ofprocessor 9 are adapted to recognize the input waveform generated by thepiezo-active sensing element 16 of the OMT sensor 1. Any waveform havingan amplitude greater than a predetermined threshold (such as that causedby microsaccades) are filtered and eliminated as not beingrepresentative of reliable OMT information.

A conventional processing technique (e.g., fast Fourier transformanalysis, linear predictive modeling or peak counting) is used tocompute the frequency of the digital OMT biosignal. In a peak countingapproach, the OMT biosignal is sampled during a predetermined timeinterval. A count of the signal peaks is maintained and incrementedduring the sampling time. The peak frequency in numerical form(designated 14 in FIG. 1) is displayed by the display 10 (best shown inFIG. 1). Likewise, a real time graphical representation of the OMTsignal waveform (designated 12 in FIG. 1) is also displayed so that arecent history of the patient's brain stem activity and level ofconsciousness is visually available at the display 10.

The frequency of the OMT biosignal being sampled is tested for validityso that spurious signals can be filtered and eliminated. For example,the frequency of the OMT biosignal can be inspected and compared with apredetermined frequency range that is known to conform to recognizedphysiological conditions. What is more, if the patient is subjected to abase line test prior to being anesthetized, the OMT biosignal can becompared with the base line test results. Any portion of the OMTbiosignal which is determined to be indicative of gross eye movementsand microsaccades is eliminated.

FIG. 18 of the drawings shows the piezo-active sensing element 16 of theOMT sensor 1 communicating with a signal processor 9-1 that is capableof receiving the amplified analog OMT biosignal from the OMT signalamplifier 3-1 over a wireless communication path. However, where theamplifier 3-1 communicates with the processor 9-1 over a wirelesscommunication path, the previously described analog-to-digital converter110 is removed from the processor (designated 9 in FIG. 17) and nowlocated in the amplifier 3-1 to receive the OMT biosignal from theribbon assembly 5. The A/D converter 110 of amplifier 3-1 of FIG. 18 isconnected to a wireless transmitter 116 which is also located in theamplifier 3-1. In this case, the shielded cable (designated 7 in FIGS. 7and 17) is eliminated. Likewise, the signal processor 9-1 of FIG. 18 isprovided with a wireless transceiver 118 which is compatible to andcapable of communicating with the wireless transmitter 116 of amplifier3-1. Thus, the processor 9-1 may be located remotely from the OMT sensor1 (e.g., at a nurses' station) so that the patient can be monitored ashe recovers from an operation or other procedure and returns toconsciousness.

It has been disclosed herein that the multiple layer piezo-activesensing element 16 of the ocular micro tremor (OMT) sensor 1 is attachedto the eyelid of the individual being tested such that the sensingelement 16 is deflected by the micromovements of an individual's eyeballto generate a biosignal. However, rather than having the micromovementsapplied from the individual's eyeball directly to the piezo-activesensing element 16 to cause a deflection thereof, the micromovements caninstead be applied to an intermediate mechanical actuator. FIG. 19 ofthe drawings shows a modified ocular micro tremor (OMT) sensor 130 whichincludes a mechanical arm actuator 132 that is attached to theindividual's eyelid so as to concentrate forces and stress on arelatively small piezo-active sensing element 134. In this case, themicromovements are applied from the eyeball to the mechanical armactuator 132 rather than directly to the sensing element.

The mechanical arm actuator 132 of the modified OMT sensor 130 of FIG.19 is preferably manufactured from a non-conductive medical gradeplastic. The mechanical arm actuator 132 is attached to the individual'sclosed eyelid so as to conform to the shape of the eyelid at which to bedeflected in response to the micromovements of the individual's eyeball.The piezo-active sensing element 134 of FIG. 19, which may be identicalin construction to the sensing element 16 shown in FIGS. 8-10, islocated between the mechanical arm actuator 132 and the flexible ribbonassembly 5. The flexible ribbon assembly 5 may be identical to thatpreviously disclosed when referring to FIG. 13 and, therefore, the samereference numeral has been used therefor in FIG. 19. However, since itis now the lever advantage offered by the flexible mechanical armactuator 132 of OMT sensor 130 which causes the piezo-active sensingelement 134 to be deflected, the sensing element 134 can be made smallerand require less shielding when compared to the size and shieldingassociated with the sensing element 16. Moreover, the mechanical armactuator 132 which is not subjected to electrical or electromagneticinterference need not be shielded.

The deflection of the mechanical arm actuator 132 in response to themicromovements of the individual's eyeball through the individual'seyelid below actuator 132 is transmitted to the adjacent piezo-activesensing element 134. The biosignal generated by the sensing element 134is supplied to the amplifier (designated 3 in FIGS. 11 and 12) by way ofthe flexible ribbon assembly 5 as previously described.

An ocular micro tremor (OMT) sensor 140 having a surface-mountedpiezo-active sensing element 142 is described while referringconcurrently to FIGS. 20-23 of the drawings. However, the piezo-activesensing element 142 of sensor 140 is a tubular sleeve rather than a pairof flexible planar films as in the case of piezo-active sensing element16 of FIGS. 8-10. More particularly, the tubular sleeve sensing element142 is subjected to having its original tubular shape distorted in orderto generate a biosignal in response to the micromovements of theindividual's eyeball. That is, as is best shown in FIG. 21, the tubularpiezo-active sensing element 142 of OMT sensor 140 includes a flexible,electrically conductive interior area 144 which functions as a firstelectrical terminal. The electrically conductive interior area 144 ofsensing element 142 is surrounded by a flexible intermediatepiezoelectric material 146 that is adapted to be compressed anddeformed. An electrically conductive exterior surface 148 surrounds theintermediate piezoelectric material 146. The electrically conductiveouter surface 148 of the sensing element 142 which functions as a secondelectrical terminal may be surrounded by shielding material (not shown).By way of example only, each of the electrically conductive interiorarea 144 and exterior surface 148 (i.e., the first and second terminals)of the tubular piezo-active sensing element 142 of the OMT sensor 140 ismanufactured from a thin electrically conductive metal mesh.

The tubular surface-mounted piezo-active sensing element 142 of themicro tremor sensor 140 is located in the folds of the individual'seyelid where it will be responsive to the micromovements of theindividual's eyeball transmitted through the eyelid so as to undergo acompression and a deformation by which to generate a correspondingvoltage. With the tubular piezo-active sensing element 142 initially ina relaxed state, the electrically conductive interior area 144 andexterior surface 148 as well as the intermediate piezoelectric material146 lying therebetween all have a cylindrical configuration (not shown).However, when the tubular sensing element 142 receives a compressiveforce in response to micromovements of the individual's eyeball, theshape of each of the interior area 144, exterior surface 148 andintermediate piezoelectric material 146 is distorted and thereby assumesan elliptical configuration as shown in FIGS. 21 and 22.

The distortion and change of shape of the intermediate piezoelectricalmaterial 146 produces a biosignal between the first and second terminals(i.e., the electrically conductive interior area 144 and theelectrically conductive exterior surface 148) of the surface-mountedpiezo-active sensing element 142. The biosignal generated by the sensingelement 142 of the sensor 140 is supplied to the amplifier 3 by way of atubular-to-planar strain relief adapter 150 (of FIG. 20) of the OMTsensor 140.

Referring specifically to FIG. 23, details of the tubular-to-planarstrain relief adapter 150 of the OMT sensor 140 of FIG. 20 are shown bywhich the electrical terminals 144 and 148 of the tubular piezo-activesensing element 142 are connected to the circuit board (designated 54 inFIG. 12) of amplifier 3 in substitution of the flexible ribbon assembly3. The adapter 150 includes a flexible substrate 151 manufactured from anon-conductive material and having an arcuate (i.e., curved)configuration. The curved substrate 151 is adapted to be flexed inresponse to mechanical forces applied thereto to absorb pulling forcesthat could otherwise be applied to the piezo-active sensing element 142.A first electrically conductive trace 152 runs longitudinally along thesubstrate 151 from a first electrically conductive contact pad 154 tothe amplifier 3. A second electrically conductive trace 156 runslongitudinally along the substrate 151 from a second electricallyconductive contact pad 158 to the amplifier 3. The first and secondelectrically conductive traces 152 and 156 are arranged in spacedside-by-side parallel alignment along the non-conductive substrate 151of adapter 150 so as to be electrically isolated from one another.

The electrically conductive inner area (i.e., the first terminal 144 ofthe tubular piezo sensing element 142 is connected (e.g., pushed intolocking engagement) at a groove formed in the first contact pad 154 onsubstrate 151. The second contact pad 158 extends laterally across thesubstrate 151 so as to lie in front of and in axial alignment with thefirst contact pad 154. Therefore, at the same time that the innerconductive area 144 of the tubular piezo-active sensing element 142contacts the first contact pad 154, the electrically conductive exteriorsurface (i.e., the second terminal) 148 of the tubular sensing element142 will be automatically aligned to lie on and contact the secondcontact pad 158. Accordingly, when the tubular sensing element 142undergoes a distortion and a change of its shape in response tomicromovements of the individual's eyeball, the corresponding biosignalgenerated by the sensing element 142 between the first and secondterminals 144 and 148 thereof is transmitted for amplification to theamplifier 3 by way of respective ones of the first and second conductivetraces 152 and 156 of the strain relief adapter 150 which run along thesubstrate 151.

FIG. 24 of the drawings shows another embodiment for an ocular microtremor (OMT) sensor 160 having a mechanical actuator and a piezo-activesensing element. Like the OMT sensor 130 that was described whilereferring to FIG. 19, the sensor 160 of FIG. 24 includes a mechanicalforce transmitting actuator that is responsive to the micromovements ofthe individual's eyeball. In this case, however, rather than an armactuator attached to the individual's closed eyelid, a cylindrical forcetransmitting actuator 162 is located within the folds of the eyelid tolie closer to the eyeball than the piezo-active sensing element.

The cylindrical force transmitting actuator 162 of OMT sensor 160 isadapted to be compressed and undergo a deformation in response to themicromovements of the individual's eyeball transmitted through theindividual's eyelid. In this regard, and by way of a first example, thecylindrical force transmitting actuator 162 is manufactured from acompressible material, such as a medical grade foam rubber, or the like.By way of a second example, the cylindrical force transmitting actuator162 is filled with a compressible liquid, such as a gel, or the like. Inthe event that the cylindrical force transmitting actuator 162 is filledwith liquid, the actuator is preferably surrounded by a flexibleenvelope 164 (shown in broken lines in FIG. 24).

The ocular micro tremor sensor 160 of FIG. 24 includes a flexiblepiezo-active sensing element 166 that is generally planar so as to beadhesively attached over and conform to the shape of the cylindricalforce transmitting actuator 162. The sensing element 166 may beidentical to the piezo-active sensing element 16 that was previouslydescribed while referring to FIGS. 8-10. However, to reduce the size ofthe sensor 160, the sensing element 166 that is shown in FIG. 24includes an upper electrically conductive surface 168 which functions asa first terminal and a lower electrically conductive surface 170 whichfunctions as a second electrical terminal. An intermediate piezoelectricmaterial portion 172 is located between the upper and lower electricallyconductive surfaces 168 and 170.

The micromovements of the individual's eyeball are applied through theindividual's eyelid and result in a deformation and a change of shape ofthe cylindrical force transmitting actuator 162. The deformations of thecylindrical force transmitting actuator 162 are transmitted to theplanar piezo-active sensing element 166 which lies over and against theforce transmitting actuator 162. Accordingly, the intermediatepiezoelectric material portion 172 of the sensing element 166 iscorrespondingly deflected so that a biosignal is produced between thefirst and second terminals (i.e., the upper and lower electricallyconductive surfaces 168 and 170) lying at opposite sides of thepiezoelectric material portion 172. The biosignal may then be suppliedto an amplifier (like that designated 3 in FIGS. 11 and 12) by way of aflexible ribbon assembly (like that designated 5 in FIG. 13).

1. An apparatus comprising: a sensor comprising a piezoelectric element;and a flexible ribbon assembly comprising a conductive trace, whereinthe conductive trace is coupled to the piezoelectric element; whereinthe sensor is configured to conform to a shape of an eye registermicro-movements of an eyeball having an amplitude in an inclusive rangeof 40 micrometers to 500 nanometers.
 2. The apparatus of claim 1,wherein the sensor further comprises a conductive shield.
 3. Theapparatus of claim 1, wherein the sensor further comprises a conductiveshield and an insulator, wherein the insulator insulates the conductivetrace from the conductive shield.
 4. The apparatus of claim 1, whereinthe sensor further comprises a conductive shield and an insulator,wherein the insulator insulates the piezoelectric element from theconductive shield.
 5. The apparatus of claim 1, wherein thepiezoelectric element is 20 microns to 150 microns thick.
 6. Theapparatus of claim 1, wherein the piezoelectric element comprisesPolyvinylidene fluoride.
 7. The apparatus of claim 1, wherein the sensorfurther comprises an adhesive configured to attach to an eyelid.
 8. Theapparatus of claim 2, wherein the conductive shield comprises gold. 9.The apparatus of claim 1, wherein the sensor is further configured toregister micro-movements of an eyeball having a frequency of 84 Hz. 10.The apparatus of claim 2, wherein the conductive shield is in electricalcommunication with the conductive trace.
 11. An apparatus comprising: asensor comprising: a sensing element comprising: a piezoelectricelement; and an electrically conductive surface electrically coupledwith the piezoelectric element; and an amplifier comprising a receptacleelectrically coupled with the electrically conductive surface; whereinthe sensor is configured to conform to a shape of an eye of a patientand to register micro-movements of an eyeball having an amplitude in aninclusive range of 40 micrometers to 500 nanometers.
 12. The apparatusof claim 11, wherein the sensor further comprises a conductive shield.13. The apparatus of claim 11, wherein the sensor further comprises aconductive shield and an insulator, wherein the insulator insulates thepiezoelectric element from the conductive shield.
 14. The apparatus ofclaim 11, wherein the piezoelectric element is 20 microns to 150 micronsthick.
 15. The apparatus of claim 11, wherein the piezoelectric elementcomprises Polyvinylidene fluoride.
 16. The apparatus of claim 11,wherein the sensor further comprises an adhesive configured to attach toan eyelid.
 17. The apparatus of claim 12, wherein the conductive shieldcomprises gold.
 18. The apparatus of claim 11, wherein the sensor isfurther configured to register micro-movements of an eyeball having afrequency of 84 Hz.
 19. The apparatus of claim 12, wherein theconductive shield is in electrical communication with the electricallyconductive surface.
 20. An apparatus comprising: a sensor comprising apiezoelectric element; and a conductor, wherein the conductor iselectrically coupled to the piezoelectric element; wherein the sensor isconfigured to conform to a shape of an eye; and the sensor is configuredto register micro-movements of an eyeball having an amplitude in aninclusive range of 40 micrometers to 500 nanometers.
 21. The apparatusof claim 20, wherein the sensor further comprises a conductive shield.22. The apparatus of claim 20, wherein the sensor further comprises aconductive shield and an insulator, wherein the insulator insulates thepiezoelectric element from the conductive shield.
 23. The apparatus ofclaim 20, wherein the piezoelectric element is 20 microns to 150 micronsthick.
 24. The apparatus of claim 20, wherein the piezoelectric elementcomprises Polyvinylidene fluoride.
 25. The apparatus of claim 20,wherein the sensor further comprises an adhesive configured to attach toan eyelid.
 26. The apparatus of claim 21, wherein the conductive shieldcomprises gold.
 27. The apparatus of claim 20, wherein the sensor isfurther configured to register micro-movements of an eyeball having afrequency of 84 Hz.
 28. The apparatus of claim 21, wherein theconductive shield is in electrical communication with the conductor. 29.The apparatus of claim 1, wherein the conductive trace is in directcontact with the piezoelectric element.
 30. The apparatus of claim 11,wherein the electrically conductive surface is in direct contact withthe piezoelectric element.
 31. The apparatus of claim 21, wherein theconductor is in direct contact with the piezoelectric element.